MOST RESIDENTS of Paulsboro, N.J., who were evacuated last Friday following a train derailment that released a hazardous gas into the air were heading back home Friday.

Officials said that as of noon, air monitors had not detected any vinyl chloride for more than 24 hours, showing it was safe to end mandatory evacuations in the industrial town across the Delaware River from Philadelphia International Airport.

Residents were being allowed back only after checking in with authorities at the town's fire hall. They were accompanied by police officers to their homes, which remained behind barricades to keep nonresidents away.

Most were following officials' advice and letting experts test the air inside before moving back in.

By late afternoon, no homes had any evidence of the chemical, an ingredient in the plastic PVC, in the air.